foo.cc: In function 'void spfa(int)':
foo.cc:33:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
 for (int i=0;i<G[v].size();i++){
              ~^~~~~~~~~~~~
foo.cc: At global scope:
foo.cc:70:11: error: redefinition of 'const int MAXN'
 const int MAXN=5010;
           ^~~~
foo.cc:7:11: note: 'const int MAXN' previously defined here
 const int MAXN=5010;
           ^~~~
foo.cc:72:11: error: redefinition of 'const int INF'
 const int INF=10000000;
           ^~~
foo.cc:9:11: note: 'const int INF' previously defined here
 const int INF=10000000;
           ^~~
foo.cc:74:8: error: redefinition of 'struct edge'
 struct edge{
        ^~~~
foo.cc:11:8: note: previous definition of 'struct edge'
 struct edge{
        ^~~~
foo.cc:78:19: error: redefinition of 'std::vector<edge> G [5010]'
 vector<edge>G[MAXN];
                   ^
foo.cc:15:13: note: 'std::vector<edge> G [5010]' previously declared here
 vector<edge>G[MAXN];
             ^
foo.cc:80:11: error: redefinition of 'int d [5010]'
 int d[MAXN],n,m;
           ^
foo.cc:17:5: note: 'int d [5010]' previously declared here
 int d[MAXN],n,m;
     ^
foo.cc:80:13: error: redefinition of 'int n'
 int d[MAXN],n,m;
             ^
foo.cc:17:13: note: 'int n' previously declared here
 int d[MAXN],n,m;
             ^
foo.cc:80:15: error: redefinition of 'int m'
 int d[MAXN],n,m;
               ^
foo.cc:17:15: note: 'int m' previously declared here
 int d[MAXN],n,m;
               ^
foo.cc:82:16: error: redefinition of 'bool exist [5010]'
 bool exist[MAXN];
                ^
foo.cc:19:6: note: 'bool exist [5010]' previously declared here
 bool exist[MAXN];
      ^~~~~
foo.cc:84:11: error: redefinition of 'std::queue<int> q'
 queue<int>q;
           ^
foo.cc:21:11: note: 'std::queue<int> q' previously declared here
 queue<int>q;
           ^
foo.cc: In function 'void spfa(int)':
foo.cc:86:6: error: redefinition of 'void spfa(int)'
 void spfa(int s){
      ^~~~
foo.cc:23:6: note: 'void spfa(int)' previously defined here
 void spfa(int s){
      ^~~~
foo.cc:96:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
 for (int i=0;i<G[v].size();i++){
              ~^~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:108:5: error: redefinition of 'int main()'
 int main(){
     ^~~~
foo.cc:45:5: note: 'int main()' previously defined here
 int main(){
     ^~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。